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| Illustration 1 | g02404877 |
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Parking brake (Final Drive) (1) Passage from the brake pilot valve (2) Brake piston (3) Springs (4) Coupling (5) Plates (6) Spindle housing (7) Friction discs (8) Plate (9) Retaining ring | |
The parking brake consists of the following components: brake piston (2), springs (3), friction discs (7) and plates (5).
In the parking brake, plates (5) are splined to coupling (4). Friction discs (7) are splined to spindle housing (6).
When a travel pedal is depressed, the oil from the pump flows to the inlet port of the travel motor from the travel control valve in the main control valve. A portion of the oil from the pump flows to the shuttle valve. The oil flows from the shuttle valve to the brake pilot valve.
The brake pilot valve shifts allowing oil to flow through an internal passage of the motor head to passage (1) in spindle housing (6). The oil flows through passage (1) to the piston chamber. The oil pressure in the piston chamber overcomes the force of springs (3). The brake piston moves to the left. The spring force that is holding brake piston (2) against plates (5) and friction discs (7) is released. The parking brake is disengaged.
At the same time, oil from the pump flows through a passage and a check valve in the motor head. The oil then flows to the travel motor. The parking brake is disengaged before the travel motor starts to rotate. The output shaft of the travel motor directs power to gear within in the final drive.
When the travel pedal is returned to the NEUTRAL position, the oil from the pump is blocked at the travel control valve in the main control valve. The motor head regulates the stopping of the travel motor. The travel motor is gradually slowed to a stop.
The brake pilot valve shifts to the closed position. The force of the oil pressure on brake piston (2) is lower than the force of springs (3). The brake piston is pushed slowly to the right by the force of springs (3). The oil in the piston chamber now flows through passage (1) through an internal passage to the brake pilot valve. The oil flows through a passage in the brake pilot valve and into the motor case drain line. Friction discs (7) and plates (5) are forced together by brake piston (2). The force of springs (3) holds brake piston (2) against friction discs (7) and plates (5). Friction discs (7) are splined to spindle housing (6). Plates (5) are splined to coupling (4). When plates (5) and friction discs (7) are forced together, the parking brake is engaged. The travel motor stops rotating before the parking brake engages.
The passage in the brake pilot valve restricts return oil flow from the piston chamber. The restriction of the return oil flow delays the application of the parking brake. The parking brake is delayed in order to give the machine time to stop. Earlier wear and/or damage to the machine could result if the machine stayed in motion.